eee 
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 89 
brought down per acre in the form of ammonia was 9.936 
Ibs.; that in the form of nitric acid was 0.974 lbs. The 
total nitrogen contained in the rain, etc., was accordingly 
10.91, or, in round numbers, 11 lbs. avoirdupois. The rain- 
fall amounted to 488.309 imperial gallons, (Wilda’s Cen- 
tralblatt, August, 1866.) 
Relation of Nitric Acid to Ammonia in the Atmos- 
phere,—The foregoing results demonstrate that there is 
in the aggregate an excess of ammonia over the amount 
required to form nitrate with the nitric acid. (In nitrate 
of ammonia (NH, NO,), the acid and base contain the 
same quantity of nitrogen.) We are hence justified in 
assuming that the acid in question commonly occurs as ni- 
trate of ammonia* in the atmosphere. 
At times, however, the nitric acid may preponderate. 
One instance is on record (Journal de Pharmacie, Apr., 
1845) of the presence of free nitric acid in hail, which fell 
at Nismes, in June, 1842. This hail is said to have been 
perceptibly sour to the taste. 
Cloez (Compt. Rendus, lii, 527) found traces of free 
nitric acid in air taken 3 feet above the ground, especially 
at the beginning and end of winter. 
The same must have been true in the cases already giv- 
en, in which exceptionally large quantities of nitric acid 
were found, in the examinations made by Boussingault and 
the Prussian chemists. 
The nitrate of ammonia which exists in the atmosphere 
is doubtless held there in a state of mechanical suspension. 
It is dissolved in the falling rains, and when once brought 
to the surface of the soil, cannot again find its way into 
the air by volatilization, as carbonate of ammonia does, 
but is permanently removed from. the atmosphere, and 
* In evaporating large quantities of rain-water to dryness, there are often found 
in the residue nitrates of lime and soda. In these cases the lime and soda come 
from dust suspended in the air. 
